ioprio: rcu_read_lock/unlock protect find_task_by_vpid call (V2)
[linux-3.10.git] / fs / ioprio.c
1 /*
2  * fs/ioprio.c
3  *
4  * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
5  *
6  * Helper functions for setting/querying io priorities of processes. The
7  * system calls closely mimmick getpriority/setpriority, see the man page for
8  * those. The prio argument is a composite of prio class and prio data, where
9  * the data argument has meaning within that class. The standard scheduling
10  * classes have 8 distinct prio levels, with 0 being the highest prio and 7
11  * being the lowest.
12  *
13  * IOW, setting BE scheduling class with prio 2 is done ala:
14  *
15  * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
16  *
17  * ioprio_set(PRIO_PROCESS, pid, prio);
18  *
19  * See also Documentation/block/ioprio.txt
20  *
21  */
22 #include <linux/gfp.h>
23 #include <linux/kernel.h>
24 #include <linux/ioprio.h>
25 #include <linux/blkdev.h>
26 #include <linux/capability.h>
27 #include <linux/syscalls.h>
28 #include <linux/security.h>
29 #include <linux/pid_namespace.h>
30
31 int set_task_ioprio(struct task_struct *task, int ioprio)
32 {
33         int err;
34         struct io_context *ioc;
35         const struct cred *cred = current_cred(), *tcred;
36
37         rcu_read_lock();
38         tcred = __task_cred(task);
39         if (tcred->uid != cred->euid &&
40             tcred->uid != cred->uid && !capable(CAP_SYS_NICE)) {
41                 rcu_read_unlock();
42                 return -EPERM;
43         }
44         rcu_read_unlock();
45
46         err = security_task_setioprio(task, ioprio);
47         if (err)
48                 return err;
49
50         task_lock(task);
51         do {
52                 ioc = task->io_context;
53                 /* see wmb() in current_io_context() */
54                 smp_read_barrier_depends();
55                 if (ioc)
56                         break;
57
58                 ioc = alloc_io_context(GFP_ATOMIC, -1);
59                 if (!ioc) {
60                         err = -ENOMEM;
61                         break;
62                 }
63                 task->io_context = ioc;
64         } while (1);
65
66         if (!err) {
67                 ioc->ioprio = ioprio;
68                 ioc->ioprio_changed = 1;
69         }
70
71         task_unlock(task);
72         return err;
73 }
74 EXPORT_SYMBOL_GPL(set_task_ioprio);
75
76 SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
77 {
78         int class = IOPRIO_PRIO_CLASS(ioprio);
79         int data = IOPRIO_PRIO_DATA(ioprio);
80         struct task_struct *p, *g;
81         struct user_struct *user;
82         struct pid *pgrp;
83         int ret;
84
85         switch (class) {
86                 case IOPRIO_CLASS_RT:
87                         if (!capable(CAP_SYS_ADMIN))
88                                 return -EPERM;
89                         /* fall through, rt has prio field too */
90                 case IOPRIO_CLASS_BE:
91                         if (data >= IOPRIO_BE_NR || data < 0)
92                                 return -EINVAL;
93
94                         break;
95                 case IOPRIO_CLASS_IDLE:
96                         break;
97                 case IOPRIO_CLASS_NONE:
98                         if (data)
99                                 return -EINVAL;
100                         break;
101                 default:
102                         return -EINVAL;
103         }
104
105         ret = -ESRCH;
106         /*
107          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
108          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
109          * in copy_process().
110          */
111         read_lock(&tasklist_lock);
112         switch (which) {
113                 case IOPRIO_WHO_PROCESS:
114                         rcu_read_lock();
115                         if (!who)
116                                 p = current;
117                         else
118                                 p = find_task_by_vpid(who);
119                         if (p)
120                                 ret = set_task_ioprio(p, ioprio);
121                         rcu_read_unlock();
122                         break;
123                 case IOPRIO_WHO_PGRP:
124                         if (!who)
125                                 pgrp = task_pgrp(current);
126                         else
127                                 pgrp = find_vpid(who);
128                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
129                                 ret = set_task_ioprio(p, ioprio);
130                                 if (ret)
131                                         break;
132                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
133                         break;
134                 case IOPRIO_WHO_USER:
135                         if (!who)
136                                 user = current_user();
137                         else
138                                 user = find_user(who);
139
140                         if (!user)
141                                 break;
142
143                         do_each_thread(g, p) {
144                                 int match;
145
146                                 rcu_read_lock();
147                                 match = __task_cred(p)->uid == who;
148                                 rcu_read_unlock();
149                                 if (!match)
150                                         continue;
151                                 ret = set_task_ioprio(p, ioprio);
152                                 if (ret)
153                                         goto free_uid;
154                         } while_each_thread(g, p);
155 free_uid:
156                         if (who)
157                                 free_uid(user);
158                         break;
159                 default:
160                         ret = -EINVAL;
161         }
162
163         read_unlock(&tasklist_lock);
164         return ret;
165 }
166
167 static int get_task_ioprio(struct task_struct *p)
168 {
169         int ret;
170
171         ret = security_task_getioprio(p);
172         if (ret)
173                 goto out;
174         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
175         if (p->io_context)
176                 ret = p->io_context->ioprio;
177 out:
178         return ret;
179 }
180
181 int ioprio_best(unsigned short aprio, unsigned short bprio)
182 {
183         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
184         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
185
186         if (aclass == IOPRIO_CLASS_NONE)
187                 aclass = IOPRIO_CLASS_BE;
188         if (bclass == IOPRIO_CLASS_NONE)
189                 bclass = IOPRIO_CLASS_BE;
190
191         if (aclass == bclass)
192                 return min(aprio, bprio);
193         if (aclass > bclass)
194                 return bprio;
195         else
196                 return aprio;
197 }
198
199 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
200 {
201         struct task_struct *g, *p;
202         struct user_struct *user;
203         struct pid *pgrp;
204         int ret = -ESRCH;
205         int tmpio;
206
207         read_lock(&tasklist_lock);
208         switch (which) {
209                 case IOPRIO_WHO_PROCESS:
210                         rcu_read_lock();
211                         if (!who)
212                                 p = current;
213                         else
214                                 p = find_task_by_vpid(who);
215                         if (p)
216                                 ret = get_task_ioprio(p);
217                         rcu_read_unlock();
218                         break;
219                 case IOPRIO_WHO_PGRP:
220                         if (!who)
221                                 pgrp = task_pgrp(current);
222                         else
223                                 pgrp = find_vpid(who);
224                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
225                                 tmpio = get_task_ioprio(p);
226                                 if (tmpio < 0)
227                                         continue;
228                                 if (ret == -ESRCH)
229                                         ret = tmpio;
230                                 else
231                                         ret = ioprio_best(ret, tmpio);
232                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
233                         break;
234                 case IOPRIO_WHO_USER:
235                         if (!who)
236                                 user = current_user();
237                         else
238                                 user = find_user(who);
239
240                         if (!user)
241                                 break;
242
243                         do_each_thread(g, p) {
244                                 int match;
245
246                                 rcu_read_lock();
247                                 match = __task_cred(p)->uid == user->uid;
248                                 rcu_read_unlock();
249                                 if (!match)
250                                         continue;
251                                 tmpio = get_task_ioprio(p);
252                                 if (tmpio < 0)
253                                         continue;
254                                 if (ret == -ESRCH)
255                                         ret = tmpio;
256                                 else
257                                         ret = ioprio_best(ret, tmpio);
258                         } while_each_thread(g, p);
259
260                         if (who)
261                                 free_uid(user);
262                         break;
263                 default:
264                         ret = -EINVAL;
265         }
266
267         read_unlock(&tasklist_lock);
268         return ret;
269 }